diff --git a/tools/.gitignore b/tools/.gitignore
index 901df7b..f8ae9ea 100644
--- a/tools/.gitignore
+++ b/tools/.gitignore
@@ -10,3 +10,4 @@
 /exec
 /blkpack
 /blkunpack
+/blkup
diff --git a/tools/blkup.c b/tools/blkup.c
new file mode 100644
index 0000000..25dffb5
--- /dev/null
+++ b/tools/blkup.c
@@ -0,0 +1,67 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+#include "common.h"
+
+/* Push specified file to specified device blk device, starting from blkno
+ * and upwards.
+ */
+
+int main(int argc, char **argv)
+{
+    if (argc != 4) {
+        fprintf(stderr, "Usage: ./blkup device blkno fname\n");
+        return 1;
+    }
+    unsigned int blkno = strtol(argv[2], NULL, 10);
+    FILE *fp = fopen(argv[3], "r");
+    if (!fp) {
+        fprintf(stderr, "Can't open %s.\n", argv[3]);
+        return 1;
+    }
+    int fd = open(argv[1], O_RDWR|O_NOCTTY|O_SYNC);
+    if (fd < 0) {
+        fprintf(stderr, "Could not open %s\n", argv[1]);
+        return 1;
+    }
+    set_interface_attribs(fd, 0, 0);
+    set_blocking(fd, 1);
+    char s[0x40];
+    char buf[1024] = {0};
+    sendcmdp(fd, ": _ 1024 0 DO KEY DUP .x I BLK( + C! LOOP ;");
+
+    int returncode = 0;
+    while (fread(buf, 1, 1024, fp)) {
+        sendcmd(fd, "_");
+        for (int i=0; i<1024; i++) {
+            putchar('.');
+            fflush(stdout);
+            write(fd, &buf[i], 1);
+            usleep(1000); // let it breathe
+            mread(fd, s, 2); // read hex pair
+            s[2] = 0; // null terminate
+            unsigned char c = strtol(s, NULL, 16);
+            if (c != buf[i]) {
+                // mismatch!
+                fprintf(stderr, "Mismatch at bno %d (%d) %d != %d.\n", blkno, i, buf[i], c);
+                // we don't exit now because we need to "consume" our whole program.
+                returncode = 1;
+            }
+            usleep(1000); // let it breathe
+        }
+        readprompt(fd);
+        if (returncode) break;
+        memset(buf, 0, 1024);
+        sprintf(s, "%d BLK> ! BLK!", blkno);
+        sendcmdp(fd, s);
+        blkno++;
+    }
+    sendcmdp(fd, "FORGET _");
+    printf("Done!\n");
+    fclose(fp);
+    return returncode;
+}
+
diff --git a/tools/common.c b/tools/common.c
index 0de4532..e029df0 100644
--- a/tools/common.c
+++ b/tools/common.c
@@ -16,10 +16,22 @@ void mread(int fd, char *s, int count)
     }
 }
 
+void mexpect(int fd, char ec)
+{
+    char c;
+    mread(fd, &c, 1);
+    if (c != ec) {
+        fprintf(stderr, "Expected %d but got %d\n", ec, c);
+    }
+}
+
 void readprompt(int fd)
 {
-    char junk[3];
-    mread(fd, junk, 3); // " ok" prompt
+    mexpect(fd, ' ');
+    mexpect(fd, 'o');
+    mexpect(fd, 'k');
+    mexpect(fd, '\r');
+    mexpect(fd, '\n');
 }
 
 void sendcmd(int fd, char *cmd)
@@ -34,14 +46,14 @@ void sendcmd(int fd, char *cmd)
         usleep(1000);
     }
     write(fd, "\r", 1);
-    mread(fd, junk, 2); // sends back \r\n
+    mexpect(fd, '\r');
+    mexpect(fd, '\n');
     usleep(1000);
 }
 
 // Send a cmd and also read the " ok" prompt
 void sendcmdp(int fd, char *cmd)
 {
-    char junk[2];
     sendcmd(fd, cmd);
     readprompt(fd);
 }